[ALSA] usbaudio - remove urb->bandwidth reference

Recent changes in usbcore removed the bandwidth field from struct urb.
Remove the occurence in usbaudio.c

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>